In the range of questions, this leans to mostly conceptual. 

What are the reasons for keeping original data columns once new "clean" columns have been saved?  During class, we discussed it is because the original columns will be useful during further cleaning steps. 

The situation that's motivating this question is:  I'm getting annoyed with how wide the entire dataframe is getting after adding "clean" columns.  I almost want to create another dataframe for just the clean columns to address the issue but iterating through two different dataframes sounds like it will raise it's own challenges. 

Why keep the old columns once I have nice clean columns?